1. Field of the Invention
The invention relates to a hybrid vehicle having an internal combustion engine and an electric motor as drive power sources and having a continuously variable transmission as a transmission and, more particularly, to a control apparatus that performs torque assist using the electric motor at the time of a speed shift such as a downshift or the like.
2. Description of the Related Art
In vehicles (driven only by an internal combustion engine) equipped with a continuously variable transmission (hereinafter, referred to as xe2x80x9cCVTxe2x80x9d) and, more particularly, a CVT having a belt-type continuously variable shift apparatus, the shift inertia is generally great due to the movement of a pulley that has a certain weight, securement of an oil pressure as a pulley pressing force, etc. Furthermore, the engine revolution speed is generally set so as to achieve a relatively low speed state where the fuel economy optimizes. Therefore, when a driver depresses a throttle (accelerator) pedal for a downshift, the engine torque reduces and the response and the output torque characteristic reduce due to the shift inertia and the low engine revolution speed setting mentioned above, so that the driver perceives an uncomfortable acceleration feel.
As described in Japanese Patent Application Laid-Open No. 2000-23309, a control apparatus of a hybrid vehicle having an internal combustion engine and an electric motor (motor generator) has been proposed. The control apparatus includes a CVT and a torque combining-distributing mechanism formed by a planetary gear unit. If there is a shift request for the CVT and there is an acceleration request, the control apparatus supplementally provides a margin torque needed for increasing the rotation speed inputted to the CVT by using a torque outputted from the motor during a shift transition of the CVT.
The above-described hybrid vehicle control apparatus is designed for a case where there is a downshift operation with the amount of accelerator operation exceeding 80[%] while a sports pattern, that is, a high speed with a high responsiveness, has been selected. In that case, since a torque greater than the maximum engine torque is needed, the control apparatus adds a torque corresponding to the difference from the torque determined by a movement locus of the engine operation point, by using the electric motor. Thus, the control apparatus is not intended to resolve the degradation of acceleration feel caused by the aforementioned great shift inertia of the CVT.
Moreover, in the above-described hybrid vehicle control apparatus, the shift speed of the CVT is set to a predetermined speed when there is a request for acceleration. The control apparatus is designed to compensate for a torque shortage at, the time of a downshift at the aforementioned shift speed by using the electric motor. That is, the control apparatus is designed for a hybrid vehicle equipped with a large electric motor having a sufficient margin. Thus, in the control apparatus, no consideration is made regarding a case where the assist torque from the motor cannot compensate for a torque shortage at the time of a downshift.
Accordingly, it is an object of the invention to provide a hybrid vehicle control apparatus that allows a quick speed by assisting with a torque from an electric motor and, in a case where the assist torque from the motor is insufficient in quantity, allows a shift at a shift speed in accordance with the case, thereby resolving the degradation of acceleration feel caused by the shift inertia of the CVT.
According to the invention, there is provided a hybrid vehicle control apparatus for a hybrid vehicle including an internal combustion engine and an electric motor as drive power sources and including a continuously variable transmission as a transmission for transferring a drive power to a drive wheel. The hybrid vehicle control includes means for setting a maximum shift target changing rate of the continuously variable transmission based on a shift request from an operating person, means for setting an assist torque needed for achieving the maximum shift target changing rate, means for comparing the assist torque and a torque outputtable by the electric motor, and means for restricting a target changing rate of the continuously variable transmission based on a ratio between the assist torque and the electric motor torque if the assist torque is greater than the electric motor torque.
The control apparatus of the invention operates, for example, in the following manner. That is, if a driver depresses an accelerator pedal to make a request for a shift, such as a downshift or the like, the maximum shift target changing rate (shift speed) of the continuously variable transmission (CVT), such as a belt-type continuously variable shift apparatus, is set based on the shift inertia of the CVT and the like. An assist torque is set by subtracting the normal torque of the internal combustion engine from the torque needed to achieve the maximum shift target changing rate. The assist torque is compared with the torque outputtable by the electric motor based on the characteristic of the motor. If the assist torque is greater than the motor torque, the target changing rate is restricted by an assist possible rate based on the ratio between the assist torque and the motor torque. With reference to the target changing rate (shift speed), the shifting of the CVT is controlled.
According to the above-described hybrid vehicle control apparatus of the invention, torque assist is performed by using the electric motor at the time of a shift operation of the continuously variable transmission, such as a downshift or the like, so that the uneasy feeling caused by reduction in response and output torque can be reduced or substantially avoided. If the output torque of the electric motor is less than the assist torque, the target changing rate is restricted by the ratio between the electric motor torque and the assist torque, so that the shift operation of the continuously variable transmission can be achieved at a shift speed corresponding to the electric motor output without causing ,an output torque reduction due to belt slip or the like. Thus, it becomes possible to provide a hybrid vehicle equipped with a relatively small-capacity electric motor.
In the hybrid vehicle control apparatus, the continuously variable transmission may have a belt-type continuously variable shift apparatus, and the maximum shift target changing rate may be set based on a shift inertia of the belt-type continuously variable shift apparatus.
Therefore, it becomes possible to apply the continuously variable transmission equipped with a highly reliable belt-type continuously variable shift apparatus to a hybrid vehicle and perform shifting without causing uneasy feeling. That is, the belt-type continuously variable shift apparatus has been put into practical use as a highly reliable continuously variable transmission. Furthermore, although the belt-type continuously variable shift apparatus has a relatively great shift inertia due to its construction, the maximum shift target changing rate is set by the shift inertia of the belt-type continuously variable shift apparatus in this invention.
Furthermore, in the hybrid vehicle control apparatus, the shift request from the operating person may be for a downshift.
Therefore, it becomes possible to perform a quick downshift due to the assist torque from the electric motor although a downshift is normally performed due to a sharp torque request from a driver and therefore requires a quick shift operation.
Still further, in the hybrid vehicle control apparatus, the continuously variable transmission may have a torque converter, and the electric motor may be contained together with the torque converter within a converter housing, and may be disposed on an outer peripheral portion of a front cover of the torque converter, and a rotor of the electric motor may be connected to the front cover and an output shaft of the internal combustion engine.
In this construction, the electric motor is disposed on an outer peripheral portion of the front cover of the torque converter, so that the electric motor can be disposed in a compact fashion. Hence, it becomes possible to dispose the electric motor in an installation space approximately equal the conventionally required space without a need to considerably modify a conventional transmission. Thus, it is possible to provide a hybrid vehicle without considerably changing the vehicle structure.
Still further, in the hybrid vehicle control apparatus, the continuously variable transmission may include a torque converter, a forward-reverse switching apparatus, and a primary pulley of the belt-type continuously variable shift apparatus that are disposed on a first axis A aligned with an output shaft of the internal combustion engine, and a secondary pulley of the belt-type continuously variable shift apparatus, and the electric motor may be disposed on a second axis B parallel to the first axis A.
In this construction, the electric motor is disposed on the second axis B (the secondary side) where there is a relatively large margin in the axis-direction dimension in a continuously variable transmission having a belt-type continuously variable shift apparatus. Therefore, it is possible to provide a compact hybrid vehicle in which increases in dimensions are prevented particularly in the direction of the axis.
Further, in the hybrid vehicle control apparatus, the electric motor may be a motor generator.
Since the electric motor is a motor generator, the electric motor is able to serve not only as a motor for assisting the internal combustion engine but also as a generator for performing electric charging when energy regeneration during braking is possible or when the internal combustion engine has a reserve capacity. Furthermore, the electric motor can also be used as a starter motor to start the internal combustion engine. Therefore, it is possible to improve fuel economy and achieve cleaner exhaust gas.